Polyalkenyl acylating agents, most notably polyisobutenyl succinic acids and anhydrides, are known intermediates for the preparation of products useful as additives in lubricants, fuels, and functional fluids. In particular, succinamide and succinimide products produced by the reaction of monoamines or polyamines with polyalkenyl succinic anhydrides have been employed as ashless dispersants and detergent additives in lubricating oils and in fuels. Succinic esters produced by the reaction of monoalcohols or polyols with polyalkenyl succinic anhydrides have also been used as ashless dispersants and detergents.
Polyalkenyl acylating agents have previously been prepared using a one-step halogen-assisted reaction process in which a polyalkene and an enophile are reacted at elevated temperature in the presence of chlorine. Such materials have also been prepared using a two-step halogen-assisted process in which the polyalkene is chlorinated in the first step and the resulting chlorinated polyalkene is then reacted with the enophile at elevated temperature. Both the one- and two-step chloro processes can produce polyalkenyl acylating agents in relatively high yields. However, these products typically contain residual chlorine, and environmental concerns related to chlorine-containing materials make the use of the chloro processes undesirable.
The polyalkenyl acylating agents have also been prepared by the direct thermal reaction of a polyalkene and an enophile, often referred to in the art as the thermal (or “ene”) process. While the thermal process has the advantage of avoiding the use of chlorine, the reaction tends to proceed only slowly and with low yields at reaction temperatures below about 150° C. At higher reaction temperatures, the yield of the thermal process typically improves, but remains below those achieved by the halogen-assisted reaction process.
Improved thermal process yields have been achieved using polyalkene reactants having a relatively high proportion of terminal double. Terminal double bonds, particularly terminal vinylidene bonds, in polyalkenes are recognized to be generally more reactive in the thermal process than internal double bonds. U.S. Pat. No. 4,152,499, for example, discloses that adduct formation between maleic anhydride and polyisobutene occurs virtually only between maleic anhydride and a terminal double bond. U.S. Pat. No. 4,152,499 further discloses that double bonds in the β position are also capable of reacting to a certain degree, while virtually no reaction occurs at double bonds further removed from the chain ends. U.S. Pat. No. 4,086,251 discloses that terminal vinylidene is believed to be the most reactive of the terminal double bonds in polybutenes. Conventional polyisobutenes, formed by cationic polymerization using aluminum chloride catalysts such as AlCl3, generally have a relatively low content of terminal double bonds. Polyisobutenes having a high content of terminal double bonds, so-called “reactive” polyisobutenes, have been achieved by BF3-catalyzed polymerization of isobutene. Other polyalkenes having a high content of terminal double bonds (e.g., ethylene-α-olefin copolymers and α-olefin homo- and copolymers) prepared by polymerization of the corresponding monomers in the presence of metallocene catalyst systems have also been disclosed.
Both the halogen-assisted and thermal reactions described above also tend to produce significant amounts of a sediment byproduct which must be filtered from the final product prior to its use as an additive or intermediate. The thermal process also tends to produce tars, which coat the reactor walls, necessitating frequent, time-consuming, and therefore costly clean-ups of the reactor vessel. Sediment and tar formation is believed to be due, at least in part, to the decomposition and/or polymerization of the unsaturated enophile, which has typically been maleic anhydride.
U.S. Pat. No. 3,412,111 describes a process for reacting olefin monomer with maleic anhydride in the presence of either a hydroxyl aromatic compound, or an amino aromatic in order to prevent an unwanted olefin polymerization side reaction. Similar disclosures are made in each of EP-A-0 319 809 A2 and EP-A-0 359 316 B1.
U.S. Pat. Nos. 3,960,900; 4,029,592 and 4,086,251 describe the halogen-assisted reaction of polybutene and maleic anhydride in the presence of a halogenated hydrocarbon and other halogenated compounds wherein yield was improved and tar formation was decreased. U.S. Pat. No. 3,960,900 further describes the use of phenothiazine, in combination with the halogenated hydrocarbon or compound. It is noted that the use of phenothiazine alone is able to reduce tar and increase yield somewhat, but that these improvements are not as great as when the phenothiazine and halogenated hydrocarbon or compound are used simultaneously. No effect on sediment is suggested, and the patent notes that the final product must be filtered.
In association with the practice of the thermal reaction the use of certain additives to reduce the formation of tars and sediments is known. For example, U.S. Pat. No. 4,235,786 discloses that sediment formation in the thermal reaction can be markedly reduced by the presence of a sediment-reducing amount of an oil-soluble strong organic acid. The patent discloses that the oil-soluble strong organic acid is preferably a C15-C70 optimally C28-C36 hydrocarbyl substituted sulfonic acid. U.S. Pat. No. 5,777,025 describes a process in which a thermal reaction is conducted at elevated temperature and pressure in the presence of a sediment-inhibiting amount of an oil soluble hydrocarbyl-substituted sulfonic acid.
While the use of the thermal reaction and highly reactive polymer has been found to reduce tar and sediment formation, and the presence of sulfonic acid has been found to further ameliorate tar and sediment formation, there remains a continuing need for improved thermal processes that completely eliminate, or further reduce the amount of sediments and/or tars, most particularly sediment, such that the filtration of the reaction product is more easily accomplished, or becomes unnecessary.